Android:网络连接检查总是失败

<uses-permission android:name="android.permission.INTERNET" />

ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();
if (networkInfo != null && networkInfo.isConnected()) {
    // 网络连接正常
} else {
    // 网络连接失败
}

System.setProperty("dns.server", "8.8.8.8"); // 设置DNS服务器为Google的公共DNS服务器

System.setProperty("http.proxyHost", "proxy.example.com"); // 设置HTTP代理服务器
System.setProperty("http.proxyPort", "8080"); // 设置HTTP代理服务器端口

int timeout = 5000; // 设置超时时间为5秒
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setConnectTimeout(timeout);
connection.setReadTimeout(timeout);